1. Field of the Invention
The present invention relates to a semiconductor laser device and a method of manufacturing the same, and relates more particularly to a broad-area type semiconductor laser device in which light intensity distributions of a near field pattern (hereafter, referred to as NFP) and a far field pattern (hereafter, referred to as FFP) are uniform, and to a method of manufacturing such a semiconductor laser device.
2. Description of Related Art
The broad-area type semiconductor laser device in which a stripe width is larger than 10 μm is frequently used for a light source of a laser printer or a display apparatus, as a high output type semiconductor laser device.
Here, the configuration of a conventional AlGaAs-based broad-area type semiconductor laser device is described with reference to FIG. 5. FIG. 5 is a sectional view showing the configuration of the AlGaAs-based broad-area type semiconductor laser device. A conventional AlGaAs-based broad-area type semiconductor laser device 10 (hereafter, referred to as a conventional semiconductor laser device 10) is the semiconductor laser device for oscillating a laser light whose wavelength is 780 nm. As shown in FIG. 5, this has the multilayer structure composed of an n-Al0.7Ga0.3As clad layer 14, an n-Al0.3Ga0.7As guide layer 16, an Al0.1Ga0.9As active layer 18, a p-Al0.3Ga0.7As guide layer 20, a p-Al0.7Ga0.3As clad layer 22 and a p-GaAs cap layer 24, which are grown sequentially on an n+-GaAs substrate 12.
In the multilayer structure, the upper layers of the p-GaAs cap layer 24 and the p-AlGaAs clad layer 22 are processed as striped ridges, and n-GaAs current block layers 26 are embedded on both sides of the ridges. A p-side electrode 28 is formed on the p-GaAs cap layer 24 and the n-GaAs current block layer 26, and an n-side electrode 30 is formed on the rear surface of the n+-GaAs substrate 12.
When the above-mentioned conventional semiconductor laser device is manufactured, the n-Al0.7Ga0.3As clad layer 14, the n-Al0.3Ga0.7As guide layer 16, the Al0.1Ga0.9As active layer 18, the p-Al0.3Ga0.7As guide layer 20, the p-Al0.7Ga0.3As clad layer 22 and the p-GaAs cap layer 24 are epitaxially grown sequentially on the n+-GaAs substrate 12 by using a metal organic chemical vapor deposition method (MOCVD method) and the like. Consequently, the multilayer structure is formed. Next, in the multilayer structure, the upper layers of the p-GaAs cap layer 24 and the p-AlGaAs clad layer 22 are etched to thereby form the striped ridges. Subsequently, the n-GaAs current block layers 26 are embedded and grown on both sides of the ridges, and the ridges are embedded. Next, the p-side electrode 28 is formed on the p-GaAs cap layer 24 and the n-GaAs current block layer 26, and the rear surface of the n+-GaAs substrate 12 is polished to thereby adjust the thickness of the substrate. After that, the n-side electrode 30 is formed on the rear surface (for example, refer to a non-patent document 1).
The lateral mode of the laser light emitted from the semiconductor laser device has a large influence on the suitability of the device property of the semiconductor laser device when the semiconductor laser device is applied as the light source. In short, the lateral mode control to stably control the light mode in the lateral direction of the laser light emitted from the semiconductor laser device to a basic (0-th) mode is one of the important points for the control of the semiconductor laser device. In particular, the broad-area type semiconductor laser device as mentioned above has the wide stripe width. Thus, the lateral mode is apt to be a multi mode. Hence, it is difficult that the light intensity distributions of the NFP and the FFP become uniform. If the semiconductor laser device, in which the light intensity distributions of the NFP and the FFP are not uniform, is used as the light sources for printing and the like, the irregularity in the light intensity is brought about to thereby bring about the irregularity in printed characters. Also, if this is applied to a display, the image quality of a displayed image is deteriorated.
[Non-Patent Document 1]
“Basics and Application of Understandable Semiconductor Laser Device” Written by Shoji Hirata, Edited by Ohmsha Ltd. in 2001, pages 180 to 182.